Normally, antennas employ an active module, which produces heat during communication. The heat is mostly produced at a power amplifier taking part of a transmission circuit. As the power amplifier has a larger output or a lower efficiency; the power amplifier produces more heat. Especially, for a mobile satellite antenna attached to a moving object, a radome, which is a cover of the mobile satellite antenna used to protect an antenna module including the active module. The radome thermally isolates the internal part of the radome from outer condition.
The radome is normally made of fiber reinforced plastic or honeycomb panel. Since the fiber reinforced plastic has a low heat conductivity lower than 1 W/m-k, but its thickness is around 2˜3 mm, it is possible to expect heat transmission to some extent. For low frequency transceiver antennas, radomes made of inexpensive fiber reinforced plastics are normally used. In case of using the honeycomb panel to form the radome, strength increase is relatively greater than the weight increase. However, since the gap between the skins of the honeycomb panel is mostly filled with air which can not transfer heat very well, and a honeycomb structure having very low thermal conductivity and a honeycomb core's small cross section connects the skins, it is hard to expect any heat transfer through the honeycomb panel.
The underbody cover which forms the base of the antenna module and is connected to the radome is normally made of the fiber reinforced plastic or metal. In case of using the fiber reinforced plastic, the underbody cover can not perform a function as a supporting structure but only as a protection cover of the antenna module. For this reason, the underbody cover does not have to be strong enough to work as a supporting structure, and this allows minimization of the thickness to expect some extent of heat discharge. In case of using the metal, the underbody cover works as a supporting structure to attach an antenna to the moving object. Since it is metal, the heat is transferred through the underbody cover relatively well.
Conventional mobile satellite antennas do not require a power amplifier to transmit signals, because they only receive the signals. Even if the conventional mobile satellite antenna transmits the signals, since the frequency band is Ku band ranging from around 12.5 to 18.0 GHz which is relatively low, the efficiency of the power amplifier is high and the energy transformed into heat is relatively small. Also in case of manufacturing dish antennas, since there is small limitation in enlarging the size of the dish antenna, it is possible to make large ones that require the power amplifier having small power output, which leads to lower energy loss. As mentioned above, since the conventional mobile satellite antennas do not generate a lot of heat, the underbody cover is made of the metal and the radome is made of the fiber reinforced plastic, heat generated inside the antenna module can be easily transferred to the environment.
Differently from the conventional antennas, recently developed mobile satellite antennas have both functions of transmitting and receiving signals. In the aspect of frequency band, antennas are manufactured to use Ka band ranging from 26.5 to 40 GHz or both Ka and Ku bands. The heat generated from Ku band power amplifier is added to the heat generated by Ka band amplifier that has a low efficiency and generate intense heat, and the total sum of heat in the antenna module becomes an immense amount.
These days, the radome and the underbody cover are all made of honeycomb panel to lighten antenna weight for mobility. In this case, antenna is enclosed by thermally isolating material and heat produced inside the antenna is not discharged outside but is accumulated in the antenna. If the internal temperature of the antenna exceeds certain specified level, it causes damage to the antenna module, which is one cause of antenna failure.